luogu P1462 通往奥格瑞玛的道路 二分+spfa

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
const int N=50000*2;
const int mod=100000000;
int n,m,b;
int e[N],ne[N],idx,h[N],w[N];
int fi[N];
const int inf=0x3f3f3f3f;
void add(int a,int b,int c)
{
	e[idx]=b;
	w[idx]=c;
	ne[idx]=h[a];
	h[a]=idx++;
}
int dist[N];
bool st[N];
int u[N];
bool check(int mid)
{
	memset(dist,0x3f,sizeof dist);
	memset(st,0,sizeof st);
	queue<int>q;
	q.push(1);
	dist[1]=0;
	st[1]=1;
	while(q.size())
	{
		int t=q.front();
		q.pop();
		st[t]=0;
		for(int i=h[t]; i!=-1; i=ne[i])
		{
			int j=e[i];
			int w1=w[i];
			if(dist[j]>dist[t]+w1&&fi[j]<=mid)
			{
				dist[j]=dist[t]+w1;
				if(st[j]==0)
				{
					st[j]=1;
					q.push(j);
				}
			}
		}
	}
	if(dist[n]<=b)
		return true;
	else
		return false;
}
int main()
{
	memset(h,-1,sizeof h);
	cin>>n>>m>>b;
	for(int i=1; i<=n; i++)
	{
		cin>>fi[i];
		u[i]=fi[i]; 
	}
	for(int i=1; i<=m; i++)
	{
		int a,b,c;
		cin>>a>>b>>c;
		add(a,b,c);
		add(b,a,c);
	}
	sort(u+1,u+1+n);
	if(check(inf)==false)
	{
		cout<<"AFK"<<endl;
		return 0;
	}
	int l=1,r=n;
	while(l<r)
	{
		int mid=l+r>>1;
		if(check(u[mid]))
			r=mid;
		else
			l=mid+1;
	}
	cout<<u[l]<<endl;
	return 0;
}